The end of the world is nigh. That's what top astronomers will claim during a debate to end the 2011 Edinburgh International Science Festival.
Lord Martin Rees, the Astronomer Royal, believes civilisation has only a 50 per cent chance of surviving to 2100 without suffering a man-made catastrophe.
And the Astronomer Royal for Scotland, Professor John Brown, has an equally bleak outlook, fearing a random event from outer space is the most likely cause of our demise.
They will take to the stage to put forward their stark predictions in the discussion "Fire in the Sky: Cosmic Threats to Earth".
Despite having widely differing views, these two titans of astronomy between them offer global warming, over-population, terrorism, an asteroid falling to earth and a solar blast as potential reasons to panic.
Prof Brown told the Scotsman: "The threats Lord Rees and myself will be talking about are dangerous in different ways.
"Asteroids fall to earth on average 10-100 million years apart. It's been 65 million years since the last one, so one could happen next week to 60 million years from now.
"The probability in our lifetime is very small, making it low risk, high consequence.
"There's more risk of a solar blast than an giant asteroid falling, but it would not have such high consequences."
Lord Rees said: "We can't rule out by mid-century a global political realignment heading to a stand-off between new superpowers, that could be handled less well or less luckily than the Cuban missile crisis was.
"Moreover, al-Qaeda-style terrorists might some day acquire a nuclear weapon.
"If they did, they would willingly detonate it in a city, killing tens of thousands of along with themselves, and millions would acclaim them as heroes."
Fire in the Sky: Cosmic Threats to Earth, 23 April, 10am-5pm, Edinburgh University Student Union. Free.